1. Field of the Invention
The present invention is directed generally to printing duplex and simplex copy sheets from electronic page information, especially suitable for low cost electrostatographic, ink jet, ionographic or other on-demand page printers with an endless duplex paper path loop. More particularly, the disclosed invention relates to methods for more efficiently scheduling copy sheets for insertion into and imaging by an imaging apparatus located within a portion of an endless duplex paper path loop whereby the number of skipped printer pitches is minimized, for more closely spaced or continuous production of duplex and simplex copy sheets, for higher overall productivity, yet with low page buffer memory storage requirements.
2. Description of Related Art
The terminology "copiers", and "copies", as well as "printers" and "prints", is used alternatively herein. The terminology "imaging" and "marking" is used alternatively herein and refers to the entire process of putting an image (digital or analog source) onto paper. The image can then be permanently fixed to the paper by fusing, drying, or other means. It will be appreciated that the invention may apply to almost any system in which the images are made electronically, including electronic copiers.
There is disclosed herein a simple, low cost duplexing system for efficiently utilizing a printer with a simple integrated copy sheet output and duplexing return path. It is particularly suitable for a trayless, endless loop, duplexing path.
The disclosed system provides for efficient nondirectly-sequential document page copying order or sequencing yet is capable of providing collated duplex copy sets therefrom, without requiring a large number of page images to be stored in electronic memory buffers even for jobs with a large number of pages.
It is generally known that electronically inputted printers can desirably provide more flexibility in page sequencing (page, copying presentation order) than copiers with physical document sheet input. The printer input is electronically manipulatable electronic page media, rather than physical sheets of paper which are much more difficult to reorder or manipulate into a desired sequence. As also shown in the art noted hereinbelow, it is generally known that certain such reordered or hybrid document page copying orders or sequences may be copied onto a corresponding sequential train of copy sheets in an appropriate copier or printer to provide higher copying machine productivity yet correct page order copy output, especially for duplex copies made with a copier with trayless duplexing, i.e., providing a limited length endless buffer loop duplexing path for the copy sheets being duplexed. The system disclosed herein provides for improvements therein.
The Xerox Corporation "9700" printer, duplex version, for example, has a long duplex paper path, and is suited to print long jobs. It operates in essentially a trayless mode, with a long duplex loop path. Initially, prints (copies) of only the even sides are made, with one skip cycle between each print until the entire paper path is filled with even side prints alternated with skipped cycles. When the first completed even side (page 2) reaches the transfer area for the second side print (page 1), that page is printed on the back side. The next print to be made, however, is the next even side in the sequence printed on a blank sheet, and interleaved in the blank spaces (previously skipped cycles) left between sheets on the first pass. Thus, the job then proceeds at full productivity, intermixing even sides printed on blank sheets for the first pass with odd sides printed on the back of previously completed even sides on their second pass. After the last even side is printed, the system resumes the skip cycle operation until all the odd sides are printed on the last of the even side prints.
For a 30 page job, this "9700" printer duplex version page copying sequence can be represented as shown below. [Each "S" represents a skipped cycle. Previously printed sheet pages making their second pass for their second side copy are shown under the slash.]
First stage--[evens copied +skips =half productivity]: 2, S, 4, S, 6, S, 8;
Second stage--[odds and evens intermixed--full productivity]: 1/2, 10, 3/4, 12, 5/6, 14, 7/8, 16, 9/10, 18, 11/12, 20, 13/14, 22, 15/16, 24, 17/18, 26, 19/20, 28, 21/22, 30;
Third stage--[Odds copied +skips =half productivity]; 23/24, S, 25/26, S, 27/28, S, 29/30.
Note that with this "9700" printer sequence, 36 machine cycles are required to make 30 prints. So, for this 30 page job, the overall duplex operation is only 83% efficient. For longer jobs, the effective efficiency improves. But for shorter jobs the overall efficiency degrades, since there will still be 6 skipped pitches--"S".
The sequence used on Xerox Corporation "5700" printer is somewhat similar, except that it is not a trayless duplex loop system. All the completed first side sheets are stacked into a duplex buffer tray and later refed for side two printing. With this system, printer skip cycles are not required during the first stage of the job. The skip cycles are also not required for the third stage since the completed side ones can be fed at full thruput from the duplex tray. Thus, the "5700" duplexing is much more efficient than in the "9700". However, such duplex tray systems are inherently less reliable in some respects. The required duplex tray stacking, reseparating, and refeeding is implicated in the vast majority of duplex paper jams, and complicates job recovery. That is eliminated with the "9700" and other endless moving path duplex buffer loop systems.
Other conventional sequences for printers are also possible. For example, the Hewlett Packard HP "2000" uses a stack and re-feed method of duplex in which all even sides of the entire job are printed, followed by printing all of the odd sides. However, for this, the entire job (all the page images) must be stored in memory in order to insure jam recovery.
It is desirable to provide duplexing devices using the trayless duplex buffer loop technology, particularly for smaller and less expensive printers. Thus, sequences such as are used for the Xerox "5700" and HP "2000" printers are not appropriate since they require a duplex tray for the copy sheet stacking and re-feeding. The "9700" printer method is also inappropriate because of said inefficiency for short jobs. (Jobs with a small number of document pages and corresponding copy pages per set.) Short jobs predominate in many user's needs. Irrespective of the job size, the "9700" printer method always requires 6 skipped pitches: 3 for the first series of even sides, and 3 for the last series of odd sides, as discussed.
It is also desirable to provide a copy sheet sequencing schedule which is highly efficient even when a job or a series of jobs to be printed consecutively includes one or more sheet groups containing one or more simplex sheets interspersed throughout a plurality of duplex sheets. When one or more simplex sheets are to be imaged following the imaging of one or more duplex sheets, it is necessary to schedule the simplex sheets for side one imaging after scheduling the duplex sheets for side two imaging if the output order of the sheets from the imaging device must be preserved. When using an imaging device having an endless duplex paper path loop to print simplex sheets after duplex sheets, skipped pitches are usually required to be scheduled after the duplex side one scheduling until the duplex paper path loop is "filled" (i.e., filled with duplex side ones and skipped pitches). The duplex sheets imaged with side one images are then scheduled for side two imaging upon being recirculated through the duplex loop, and then the subsequent simplex sheets are scheduled in order to preserve the output order of the sheets. Thus, undesirable skipped pitches are required.
A somewhat similar situation arises when the simplex sheets precede the duplex sheets in the order of required output from the imaging system. Conventional imaging systems schedule the simplex sheets for imaging prior to scheduling the duplex sheets. Thus, if the number of duplex sheets to be imaged is less than the number of pitches contained in the endless duplex paper path loop, skipped pitches are scheduled after scheduling the duplex side ones.
Another source of inefficiencies in the overall productivity of imaging systems having an endless duplex paper path loop results when, in response to a "skip request", the imaging system does not schedule a duplex sheet in a pitch of the endless duplex paper path loop for side one imaging. A "skip request" can emanate from, for example, the paper path when a sheet of paper is not ready for insertion into the paper path, the xerographic control system, or the Input-Output Terminal (IOT) when it is informed that an image is not ready to be printed (e.g., the image to be printed has not yet been completely retrieved from memory). When a skip request is produced, an unexpected gap results in the stream of sheets scheduled for side one imaging in the duplex loop. Since these sheets are recirculated through the duplex loop for side two imaging, any unexpected gaps which exist in the side one sheet stream also exist in the side two sheet stream. The gaps in the side two sheet stream which result from unexpected gaps in the side one sheet stream are also referred to as the "back of the skip request". While the gap in sheet scheduling due to the skip request cannot be avoided, it is desirable to eliminate scheduling of the back of the skip request. If the back of the skip request can be eliminated, the number of gaps which are produced during duplex imaging due to skip requests can be reduced by 50%.
Of particular prior art interest is Mead Corporation U.S. Pat. No. 4,453,841 issued June 12, 1984 to Bobick et al disclosing a trayless duplexing buffer loop path printer system, and noting particularly the page copying sequences shown in FIG. 6, particularly for documents with more than 10 pages, e.g., the examples shown with 16 and 22 pages.
Also of particular interest for also showing page copying sequences or algorithms for a trayless buffer loop duplexing printer is Canon EP 0 295 612 Al (European patent application) published Dec. 21, 1988 by A. Noguchi et al.
The above-cited Mead Corporation U.S. Pat. No. 4,453,841 to Bobick et al is of particular interest for its apparent disclosure of a printer with a batch mode algorithm page order presentation, as particularly shown in FIG. 6 thereof. However, that algorithm appears to operate with the document pages in descending (N to 1) rather than ascending (1 to N) page order, so that printing cannot be started until the entire job is downloaded or buffered, and requiring therefore an electronic storage media of sufficient capacity to hold all the pages of the entire document set or job. If pages are bit-mapped, as with mixed graphics, a megabyte or more of memory per page may be required even with data compression and for only 300 spi. Thus, because most computers send information in ascending serial order (starting with page 1), and most printers print in that order, an expensive print server may be required to store and reverse the order to the job before printing. That is disadvantageous for a decentralized environment without a print server available, or without high baud rate downloading connecting lines from a large central computer. First copy out time can be greatly improved with 1 to N ascending page order since printing can start as soon as the first page is received rather than after the whole job is received; which can be a very long time for a multipage job sent over conventional lines, or even coaxial cable, particularly with bit mapped pages. Ascending or forward (1 to N) page order is also very helpful for duplexing, since a decision as to the last page being even or odd (simplex) does not have to be made until that last page is downloaded, nor does any separate job handling instruction have to be sent in advance for that last odd (simplex) page situation. The printer can handle that situation on its own.
U.S. Pat. No. 4,453,841 apparently converts a simplex sheet to a duplex sheet having a blank back side (see the odd document page number examples of FIG. 6 as well as col. 7, lines 42-45), but apparently only for the special situation where the last sheet of a document being coped is an odd numbered sheet. The criteria as well as the procedure for printing a simplex sheet as a duplex sheet with a blank back side are not discussed. This patent also apparently does not address the situation where a simplex sheet is located at an intermediate position within a copy set, only when it is the last sheet (or first sheet) in the set. Additionally, as demonstrated by the 16 and 22 page examples provided, skipped pitches exist between consecutive sets being scheduled.
By way of examples of further background on electronic (vs physical) page input and buffering for duplex copying or printing there is noted U.S. Pat. Nos. 4,099,254 and 4,699,503. Also, Xerox Disclosure Journal publication Vol. 8, No. 1, January/February 1983, p. 7, and its description of the Xerox "9700" duplex version laser printer and its trayless duplexing buffer loop operation. The latter and other electronic document input printers normally provide precollated output, by sequentially making one copy at a time of each document page in repeated copying "circulations" thereof, rather than making plural consecutive identical copies and utilizing sorters (post-collation). As noted in various examples in this art, and discussed further herein, there are different requirements for RDH, or pre-collation, copying vs post-collation or multicopy/sorter, copying. Maintaining collation of the documents and copies without productivity losses is a particular problem, and has been the subject of sequencing and inverting algorithms, as shown in the art.
U.S. Pat. No. 4,918,490 issued Apr. 17, 1990 to Denis J. Stemmle (Xerox Corporation) discloses an endless duplex paper path loop having a single sheet inverter for inverting sheets in the duplex loop after side one image. Sheets are consecutively inserted into the duplex loop to avoid the first and third stage skipped pitches discussed above with reference to the "9700" system. Sheets are scheduled in 1-N order, with each multipage job set being electronically divided into consecutive batches, each batch containing a small number of pages equal to approximately twice the copy sheet length.
U.S. Pat. No. 4,935,786 issued June 19, 1990 to Veeder (D.E.C.) discloses another printer having an endless duplex paper path loop with a sheet inverter. Sheets appear to be scheduled for duplex printing somewhat like the "9700" printer duplex schedule in that skipped pitches are provided during a first stage of operation. See column 3, line 46-column 4, line 14; column 6, lines 48-64; column 15, line 17-column 16, line 68; and FIG. 8. Thus, skipped pitches will exist at the beginning and end of every printing operation. This patent also appears to disclose beginning printing of one document or job unit before the last sheets of a previous document are discharged. See column 24, line 39-column 25, line 11 and FIG. 15. However, all descriptions and examples are directed to homogeneous duplex jobs. No reference is made to jobs containing simplex and duplex sheets and consequently no reference is made to handling simplex to duplex and duplex to simplex transitions.
U.S. Pat. Nos. 4,934,681 and 4,941,023 to Holmes et al (Xerox Corporation) disclose a duplex copying process wherein pitches are shuffled within the same duplex copy set for minimizing the number of skipped pitches that occur during a duplex copy cycle. A shuffling process used for a 2 pitch duplexing copy loop path length wherein pitch skips are inserted into an odd document set size duplex copy cycle and shuffling algorithms that are used to minimize pitch skips are specifically discussed for a 3 page simplex document/4 duplex copies job.
U.S. Pat. No. 4,278,344 to Sahay (Xerox Corporation) and U.S. Pat. No. 4,385,825 to Kaneko (Ricoh Co. Ltd.) disclose duplex paper path loops which are somewhat structurally similar to the present invention, but which to Britt et al (Xerox Corporation) also shows a duplex paper path loop similar to the present invention, but which includes an inverting duplex buffer tray therein. The 4,782,363 patent also discloses a type of post-collation "bindexer" unit which is usable with the present invention for collating the output from the duplex loop when necessary.
Other art of background interest includes: U.S. Pat. Nos. 4,348,101; 4,908,660; 4,845,527; and 4,681,428.
Some examples of other prior art copiers with document handlers, and especially with control systems therefor, including operator console switch selection inputs, document sheet detecting switches, etc., are disclosed in U.S. Pat. Nos.: 4,054,380; 4,062,061; 4,076,408; 4,078,787; 4,099,860; 4,125,325; 4,132,401; 4,144,550; 4,158,500; 4,176,945; 4,179,215; 4,229,101; 4,278,344; 4,284,270; and 4,475,156. It is well known in this art, and in general, how to program and execute document handler and copier control functions and logic with conventional or simple software instructions for conventional microprocessors in a copier controller. This is taught by the above and other patents and various commercial copiers. Such software may vary depending on the particular function and particular microprocessor or microcomputer system utilized, of course, but will be available to or readily programmable by those skilled in the applicable arts without experimentation, from either descriptions or prior knowledge of the desired functions together with general knowledge in the general software and computer arts. It is also known that conventional or specified document and copy sheet handling functions and controls may be alternatively conventionally provided utilizing various other known or suitable logic or switching systems.
All references cited in this specification, and their references, are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.